Recently, there has been proposed a technique regarding a pre-crash safety (PCS) system. The PCS system is driven when collision risk of an own vehicle increases to a high level in order to prevent a collision of the own vehicle with another vehicle, a pedestrian or a structure on a roadway, etc. When an incorrect calculation, used for driving the safety device, occurs due to a memory error, etc., the incorrect calculation often causes incorrect driving of the safety device.
In order to solve this problem, Patent document 1 has provided an automobile brake device. This automobile brake device has a control unit of a hierarchy structure having plural units, in which each unit calculates a braking force instruction value based on another braking force instruction value transmitted from a high hierarchy-level unit and sensor information transmitted from various sensors, and sequentially transmits the calculated braking force instruction value to a low hierarchy-level unit.
In the automobile brake device, the high hierarchy-level unit diagnoses the calculation results of the low hierarchy-level which is at one level lower. When a diagnosis result indicates that an incorrect calculation has occurred in the low hierarchy-level, the high hierarchy-level unit transmits to another lower unit at two levels lower. This control makes it possible to suppress the low hierarchy-level, in which an incorrect calculation occurs, from operating, and to drive the automobile brake device only by using the units which operate correctly.